Artificial leather manufacture



Patented Mar. 10, 1936 ARTIFICIAL LEATHER MANUFACTURE Milton 0. Schur, Berlin, N. H., assignor to Brown Company, Berlin, N. H., a corporation of Maine No Drawing. Application November 14, 1931,

- Serial No. 575,164

8 Claims.

cedure may be satisfactory in the preparation of certain kinds of artificial leather, but it gives rise to troubleywhen the artificial leather is one which is to be used as shoe upper stock and in other connections where moulding quality, ability to withstand tearing stress, ability to hold stitches, and pliancy or mellowness are required.

In an attempt to fabricate satisfactory artificial leathers of the foregoing kind, one may even have recourse to a soft, bibulofis web, which by reason of its softness and by'virtue of the resiliency inherent in rubber, is supposed to yield a product having at least pliancy or 'me1lowness,

let alone ready mouldability and high resistance to tearing stress. The fact is, however, that when latex is used as an impregnant for the web, it fails to yield a product of the desired character, especially as regards such qualities'as stitch-holding ability and pliancy or mellowness. One might expect that if the latex were loaded with a large amount of filler, thefinished article might be im paired because of dilution of the rubber, but trouble is encountered even when a straight latex is used as the impregnant. By a straight latex, I

mean either latex as obtained in nature or compounded with relatively small amountsof sulphur and vulcanization promoters. After considerable investigation, I have found that the failure of latex to yield artificial leathers of the best type is attributable to the fact that latex as derived from nature not only contains rubber hydrocarbon as the dispersed element, but has present therein certain non-rubber solids, and more es-' pecially resins, proteins, and the like. These nonrubbersolids may amount to about 1% to 5%, based on the weight of the latex, or about 3% to 15%, based on the rubber hydrocarbon. These impurities, while being without a marked effect upon the resiliency and softness of a film of evap- A orated latex, were found to exert a stiffening effect upon thefibrous foundation, even though the foundation was of a soft and fluffy character. Apparently, when a fibrous foundation is impregmated with latex, there is a tendency for the non-rubber solids to size selectively the fibrous foundation and thereby to stiffen.- it considerably.

I say this having in mind that it is possible to efiect a notable sizing and stiffening effect on paper with a comparatively small amount of rosin size and/or glue or other well-known sizing agent. The fact is, as already indicated, that straight latices do yield artificial leathers which are considerably stiffer than might reasonably be expected from a consideration of the softness of the foundation alone and the softness and pliability of the rubber coagulum alone, secured by drying latex. The foregoing conclusions were arrived at only after numerous attempts had been made to account for the faults with artificial leathers as heretofore made and to explain the variable results realized with the same fibrous foundation when different dots of latices were employed as the impregnant. Thus, the usual plasticizing agents for rubber, including oils, wax, bitumens, tars, and the like were added along with the latex to the fibrous foundation, but the resulting artificial leathers were still possessed of excessive stiffness and lacked the plump, mellow feel of well-prepared natural leathers. The failure to get anywhere with such attempts led to the conclusion that it is the non-rubber solids present in latex that make for unsatisfactory and inconsistent results.

Having determined the cause for the unsatisfactory and inconsistent results which I was securing, I found that the thing to do was to use glycerine along with the latex, as I have discovered that glycerine inhibits or prevents the stiffening orsizing of the fibrous foundation by the non-rubber solids present in the latex. In other words, I found that the way to secure the desired artificial leathers was to prevent the non-rubber solids associated with latex from exerting their stiffening and sizing effect on the fibrous web carrying the rubber. I proceeded to introduce into the latex glycerine in various amounts designed to maintain the resins and proteins associated with the latex in a permanently plastic or soft condition, wherefore when the latex was introduced into a fibrous foundation as an impregnant and was then dried, no undesirable stiffening-or sizing action on the fi-' brous foundation took place. By adding glycerine as a plasticizing or softening agent for the resins, proteins, and other impurities present in the latex, I found it possible not only to maintain in the finished leather a pliancy and mellowness characteristic of high grade natural leathers, but further to enhance vastly its resistance to tearing stress and its stitch-holding ability. My invention comprehends the use not only of glycerine, but of the homologues of glycerine, such as ethylene glycol, wherefore, the term glycerine as used in the appended claims is intended to mean glycerine and/or its homologues. Aside from the fact that the glycerine evidently acts to arrest the stiffening and sizing effect of the non-rubber solids present in the latex on the fibrous foundation, it also functions to lubricate and soften the fibers of the foundation.

I shall now give a specific example of procedure falling within the ambit of the present invention and which may be adopted in producing an artificial leather intended for use in making shoe uppers, wherein such qualities as mouldability, stitch-holding capacity, mellowness, resistance to tear, are of paramount importance. A bibulous web of interfelted fibers prepared -on machinery of the papermaking type may be used as the foundation material. The fibers are preferably of high alpha cellulose content, say at least about 93%, and derived from long-fibered wood, such as spruce. The web is preferably of comparatively low compactness, by which I mean that the fibers are substantially unbeaten and are deposited from aqueous suspension as a waterlaid web with the application of little pressure either during formation or drying. A web so made is remarkably soft, compressible, and absorbent, and can be immersed in the latex composition of the present invention, with the attainment of quick and uniform impregnation. Specifically, the latex composition can be prepared as follows. The usual ammonia-preserved latex of commerce may be converted into a vulcanized latex by adding 1%% colloidal zinc oxide, 2 colloidal sulphur, and of a suitable vulcanization accelerator, such as Pipsol-X, all based on solids content of the latex, and the mixture may be heated at substantially uniform rate from room temperature to C. within an hour, and be maintained at 60 C. for one hour. While being heated, the mixture is preferably mildly agitated and ammonia water is added to counteract the tendency toward coagulation. The vulcanized latex may then be cooled to room temperature. To the cool, prevulcanized latex may then be added 1 colloidal sulphur, 5% colloidal zinc oxide,

1% of a suitable vulcanization accelerator, such as Pipsol-X, and 15% C. P. giycerine, all based on solids content of the original latex. The prevulcanizing of the latex is thus safely carried out to a point short of that which has been found necessary for optimum results, and further vulcanization through the action of the additional vulcanizing agents is realized after the fibrous foundation has been impregnated and is subjected to drying at elevated temperature. This sort of vulcanizing procedure has,

been described and claimed in my application Serial No. 545,082, filed June 17, 1931. The latex composition containing all the elements desired for impregnation may be diluted with water to the consistency appropriate for impregnation, say a content of non-aqueous materials, including glycerine, based on total ingredients, both aqueous and non-aqueous, of about 30%. The impregnation of the web may be carried out by passing the web as a sheet of indefinite length progressively through a bath of the diluted latex composition, .wherein it need remain for only a few seconds to be impregnated uniformly throughout. The impregnated web emerging from the bath of latex composition may then be passed through a pair of squeeze rolls, which serve to remove excess latex composition from the impregnated web. The squeezed web may its faces.

then be passed through a hot-air drier maintained at 170 F. at its inlet end and at 220 F. at its exit end, wherein the speed of the web is such that it remains in contact with the heated air for about minutes. This time of contact ensures a perfectly dry web issuing from the exit end of the drier and the desired vulcanization of the rubber. The dried, impregnated web is an excellent artificial leather in the respects hereinbefore noted.

I submit hereinafter in tabulated form certain of the important characteristics of an artificial leather made in accordance with my invention as compared with an artificial leather made by the use of similar latex compositions lacking the glycerine as an added element. The tables further include the characteristics of artificial leather prepared by the use of latex compositions containing less than 15% glycerine and also more than 15% glycerine, based on latex solids.

I Series I Percent material other than glycerine added to sheet 48.0 48. 7 44. 5 47. 9 Percent glycerine used (based on latex solids); 0 2 5 10 Basis weight of final sheet- 300 290 310 Compactness 75 75 75 Tensile strength, lbs 31 34 31 Percent ultimate stretch 50 53 58 Tear resistance 580 600 665 Internal ply adhesiom. l 190 200 ness 200 l 1G0 Senes II Percent material other than glycerinc added to sheet 52. 5 4 51. 5 Percent glycerine used (based n latex solids) 0 i5 25 Basis weight of final sheet. 340 400 420 Compactness 83 d9 96 Tensile strength, lbs 46 4i 35 Ultimate stretch, perccn 33 45 57 Teal resistance 450 675 (370 Internal ply adhesion- 220 325 380 Stiflness 290 220 160 Cripples" in shoemoking test, percent"... 33% None None The results given in the foregoing tables were secured by the use as the fibrous foundation of webs of interfelted refined wood pulp fibers of the kind hereinbefore described. The webs had a basis weight of pounds and a compactness of 32. The basis weight represents the weight in pounds of 480 sheets whose dimensions are 24 x 36 inches, this being equivalent to 2880 square feet of sheet material. The compactness value iscomputed by dividing the basis weight in pounds by the thickness in inches, and multiplying by the factor 10 The meanings of the values given in the table are well known, with the possible exception of the internal'ply adhesion value, which represents the resistance to pulling apart of the artificial leather into two.

plies after the leather has been split midway of The foregoing tables show that even in the region of 5% added glycerine based on latex solids, one secures a remarkable improvement in the various important characteristics listed in the table. Evidently one'need not go above 15% added glycerine based on latex solids, for with this latex composition one secures approximately as good an improvement as can be effected by the use of more glycerine and without running into certain disadvantages incident to the use of more glycerine, such as decrease in tensile strength and difiiculty in finishing as with nitrocellulose lacquers. My invention, however,

canization accelerator, or the like, which in- 'gredients evidently do not stiffen or size the fibrous foundation, as attested by the results secured. The latices treated with the glycerine or equivalent agents may be those containing essentially only a preservative like ammonia, or socalled creamed or centrifuged latices, which are latices from which more or less non-rubber solids, including protein and resin, have been removed. As is well known, however, these purified latices necessarilycontain some residual protein,

,resins, and other impurities which operate to stifien and size a fibrous foundation impregnated with such latex, although to a less degree than ensues when normal latices are used. It will, of course, be further understood that the present invention can be applied to foundations other than those prepared on a papermaking machine, for instance, to felts or fabrics formed in a dry way on machinery of the textile type.

It is of interest to dwell on some of the properties of the glycerine-containing latex composition of the present invention. When the glycerine is absent from the composition and a vulcanized rubber film is formed therefrom by drying and heating for one hour at about 170 to 240 F., the film has a tensile strength of about 2800 pounds per square inch, and an ultimate stretch of about 100% to 800%. A similar composition containing 15% glycerine, based on latex solids, when converted into a vulcanized film under the same conditions, yields a film whose tensile strength is only 800 pounds per square inch and whose ultimate stretch is only 520%. When the glycerine content is raised to 25%, the tensile strength drops to 500 pounds per square inch, and the ultimate stretch to 500%. In short, the presence of glycerine in the vulcanized rubber film leads to a tremendous decrease in tensile strength and to a serious decrease in ultimate stretch. This observation would lead one to believe that the use of glycerine in the composition would have a most serious effect in lowering. the tensile strength and perhaps the ultimate stretch of the artificial leather. It is a most surprising fact that hardly anything is lost in tensile strength of the artificial leather, and that its ultimate stretch is actually increased markedly. The explanation for these surprising results is that the glycerine probably is more or less selectively absorbed by the fibers and hence is without appreciable effect upon the tensile properties of the rubber which occupies the interstices between the fibers.

What I claim is:

1. An artificial leather base adapted for use in making shoe upper stock consisting essentially of a fabricated, bibulous fibrous sheet impregnated and strengthened substantially throughout with rubber latex solids and containing substantially throughout sufiicient glycerine to neutralize stiffness in the base produced by latex solids but insufiicient to detract significantly from the inherent tensile strength. of the impregnated sheet.

2. An artificial leather base adapted for use in making shoe upper stock consisting essentially of an interfelted, bibulous fiber sheet impregnated and strengthened substantially throughout with vulcanized rubber latex solids and containing substantially throughout sufiicient glycerine to neutralize stifiness in the'base produced by latex solids but insufficient to detract significantly from the inherent tensile strength of the impregnated sheet.

3. An artificial leather base adapted for use in making shoe upper stock consisting essentially of an interfelted, bibulous fiber sheet impregnated and strengthened substantially throughout with rubber latex solids and containing substantially throughout sufiicient glycerine to neutralize stiffness in the base produced by latex solids but insufiicient to detract significantly from the inherent tensile strength of the im-' pregnated sheet.

4. An artificial leather base adapted for use in making shoe upper stock consisting essentially of an interfelted, bibulous cellulose fiber sheet impregnated and strengthened substantially throughout with rubber latex solids and containing substantially throughout sufficient glycerine to neutralize stifl'ness in the base produced by latex solids but insuflicient to detract significantly from the inherent tensile strength of the impregnated sheet.

5'. An arificial leather base adapted for use in making shoe upper stock consisting essentially of an interfelted, bibulous cellulose fiber sheet impregnated and strengthened substantially throughout with rubber latex solids and containing substantially throughout sufficient glycerine v to neutralize stiffness in the base produced by latex solids but insuflicient to detract significantly from the inherent tensile strength of the impregnated sheet, the cellulose fiber in said sheet comprising wood pulp fibers.

6. An artificial leather base adapted for use in making shoe upper stock consisting essentially of a bibulous, water-laid felt impregnated and strengthened substantially throughout with rubber latex solids and containing substantially throughout sufficient glycerine to neutralize stiiT- ness in the base produced by latex solids but insuificient to detract significantly from the inherent tensile strength of the impregnated felt, said waterlaid felt comprising Wood pulp fibers having an alpha cellulose content of at least about 93%. '7. An artificial leather base adapted for use in making shoe upper stock consisting essentially of a bibulous cellulose fiber sheet impregnated and strengthened substantially throughout with rubber latexsolids and containing substantially throughout glycerine in the amount of about 15% by weight, based on latex solids, to neutralize stifiness of the base produced by latex solids but without detracting significantly from the inherent tensile strength of the impregnated sheet.

8. An artificial leather base adapted for use in making shoe upper stock consisting essentially of a bibulous, waterlaid felt impregnated substantially throughout with rubber latex solids and containing substantially throughout glycerine in the amount of about 15% by weight, based on latex solids, to neutralize stiffness of the base produced by latex solids but without detracting significantly from the inherent tensile strength of the impregnated felt, said waterlaid felt comprising wood pulp fibers having an alpha cellulose content 01' at least about 93%.

METON O. SCHUR. 

